


Low Tide

by Fluffyboots



Category: Shingeki no Kyojin | Attack on Titan
Genre: Ambiguous/Open Ending, Anal Fingering, Anal Sex, Bottom Eren Yeager, Complete, Explicit Sexual Content, Human Levi (Shingeki no Kyojin), Human/Merman, Interspecies, Interspecies Awkwardness, Interspecies Sex, M/M, Mythical Beings & Creatures, Nonverbal Communication, Smut, Top Levi (Shingeki no Kyojin), auditory communication, merfolk, merman anatomy, merman eren
Language: English
Status: Completed
Published: 2018-09-23
Updated: 2018-09-28
Packaged: 2019-07-15 14:24:17
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 3
Words: 6,591
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/16064981
Author URL: https://archiveofourown.org/users/Fluffyboots/pseuds/Fluffyboots
Summary: During an afternoon walk on the beach, Levi stumbles upon a mysterious creature in need of his help.





	1. Part One

**Notes for the Chapter:**

> Thank you for clicking on my little mer fic.  
> I hope you enjoy it!

Golden sand caved in beneath his feet, the gentle shushes of the ocean offering a unique type of peace. It was a calm afternoon, air warmed by the gradual approach of Summer, a fresh sea-breeze cutting through the humid heat. Levi loved visiting the beach. It lifted his worries and alleviated his stress after a particularly painful week at the office, a rare moment of tranquility.

  
Levi kicked up grains of sand as he walked, loose ground squishing between his toes as his lungs filled with salted air. The beach was secluded. No one else cared to drive half an hour from the city straight after work, which was exactly why he did.

  
It was when Levi reached the end of the sand that he heard a peculiar noise. A quiet smacking, repetitive with the occasion click, originating from the rocky section of the beach. Eyebrows creasing, Levi turned to look around behind him. There was no one in sight. He thought it might’ve been children playing, but the lack of supervising adults was enough to convince him otherwise.

  
Levi spun on his heel to head back to his car, uninterested in whatever obscene act was going on behind those rocks. A secluded beach attracted people for all sorts of reasons. He only managed to take a few steps before a faint whistling brought him to a sudden stop. It was weird, high-pitched and squeaky like an unoiled hinge, the decidedly distressed tone giving him an odd sensation of dread.

  
Levi turned back to the rocks with a grim expression, unable to ignore what he now thought was an animal crying for help. The tide had gone out recently, ocean sitting low some distance down the beach, far out of reach for whatever was making that dreadful noise. He only hoped it was small enough for him to carry.

  
Cautious, he slowly approached the collection of rocks, their surfaces turning a light grey as they dried beneath the afternoon sun. Levi couldn’t help feeling anxious. There would be little he could do if it turned out to be a large animal, and the sound it was making was awfully similar to that of a dolphin. Levi put a hand on one of the rocks as he went past it, the pitchy whistle gradually increasing in volume, until he finally rounded the last obstruction.

  
“Holy shit,” Levi whispered, wide eyes glued to the creature writhing around in the shallow sand.

  
It definitely wasn’t a dolphin.

 

 

Levi was reluctant to name it, his mind struggling to comprehend what he was currently looking at. There was a long tail, muscular and covered in shimmering green scales, connecting to the tan skin of a human torso. It was face down and squirming weakly. A tangle of damp chestnut hair clung to the sides of its head, littered with specks of sand, two large fin-like ears protruding from either side.

  
The creature went deathly still of a sudden. Levi considered poking it with his foot, but before he could follow through it started thrashing about wildly, tail flailing as it sent sand scattering through the air.

  
It eventually rolled onto its back, exhausted, revealing a flat chest and muscled abdomen. A man… a merman. Levi felt obligated to pinch himself. He flinched as the merman’s eyes flew open, revealing the most stunning shade of turquoise he’d ever seen.

  
They watched him intently, wide and fearful, until the merman whined and rolled back onto his stomach with a dull thud. He made a futile attempt to pull himself along with his arms, while his muscular tail raised in the air before being forced back down, creating the smacking noise Levi heard earlier. The delicate flukes at the end of it swished from side-to-side as they failed to find friction, ultimately digging itself a small grave in the sand.   

  
Levi watched him struggle as he considered the situation. For now, he decided to ignore the fact that creatures like this weren’t supposed exist and focus on finding a way to help. The merman wasn’t facing towards to sea. Instead, it seemed like he was trying to wiggle his way up the beach, which was odd considering they were aquatic. Was the sun disorientating him? Levi glanced at the water behind him, sitting at its lowest point and separated by about a hundred metres of scorching sand, then looked back at where the merman was trying to go. There were plenty of large rocks, the bases of them covered in limp algae and wiry moss.

  
“Why do you want to go up there?” Levi asked, speaking to himself more than anything, and was caught off guard when the merman stopped moving and turned to stare back at him.

  
Messy brown hair was plastered over his face, blinking rapidly to keep the stray sand out of his eyes. He made the same whistling noise, eyebrows furrowing as his tail gave the ground a demanding slap.

  
Levi had no idea what the merman was trying to say, but it seemed like he was hoping for some sort of assistance. Carefully, Levi stepped closer and bent down, putting a hand on either side of his waist. There was no negative reaction. The merman simply resumed his movement, almost knocking Levi over with the force of his writhing tail. Taking it as his cue, Levi dug his heels into the sand and helped push him up the beach.

  
He was heavier than his slender form suggested, which Levi assumed was due to the sheer amount of muscle that was packed into that ornate tail. The merman’s arms did most of the work in an impressive display of upper body strength, but still needed some help moving the dead weight that dragged along behind him.

  
Once they’d managed to move a few metres, Levi spotted a large rockpool nearby. The merman’s venture suddenly made sense. He must’ve got trapped on the beach and was trying to take shelter until the tide came back in. Levi strained as he helped drag him the rest of the way, breathing heavily by the time they reached their destination. The merman let out enthusiastic whistles and clicks, clawed hands grabbing at the rocks as he tried to crawl over them. Levi made one last effort to circle his arms around the thickest part of the tail, groaning as he hoisted it up and over the barrier.

  
The merman tumbled into the rockpool with a violent splash, joyfully rolling around in the water before he propped himself up against the side. His head tilted, inspecting the pool with a pout on his face, apparently disappointed by the depth of it.

  
Levi stood beside the rocks, watching tan hands paddle about in the water. The merman looked a lot prettier now that all the sand was washed off, hair no longer plastered to his face and allowing Levi to get a proper look at it. He could see why these creatures were renowned for their captivating beauty. “Do you have a name?”

  
The merman whistled in his throat, giving Levi a questioning look as he continued wading.

  
Levi kept forgetting that he couldn’t speak back, or at least that’s the impression he got. The idea of naming him like he was a pet was off-putting… but not having something to call him was quite an inconvenience. After considering it for a moment, Levi decided to refer to the merman as _Eren_. It was from a book he’d read recently. Fitting, he thought. Levi quite liked the name and he’d never met anyone that went by it. “Eren,” Levi tested, curious of how the merman would react.

  
The newly assigned Eren stopped playing in the water to stare up at Levi, turquoise eyes shiny and fond, smiling as he warbled a short tune.

  
Levi was sure the name didn’t mean anything to him. Perhaps Eren had liked the gentle tone he’d used.

  
Levi had no idea what he should do now. The situation felt completely surreal, as if he would wake up from this bizarre dream any second now. Sighing, he turned to glance back at where they’d come from. They were surrounded by smooth rocks, almost enclosed within them, the ocean rolling in the distance while the rest of the beach was hidden from view. Looked back to Eren, Levi was a bit unsettled by how the merman was quietly staring at him. He took a step back, running a hair through his hair. “Uh… Goodluck, I guess.”

  
Eren tilted his head, tail flicking out of the water as he watched Levi move further away. Catching on, Eren clambered across in the pool until his hands were resting on the edge closest to the ocean and peeked over it. Eren clicked quietly, a nervous chatter, forlorn eyes staring out to sea before they turned back to Levi, pleading.

  
Although Levi had never been very good at picking up on the emotions of others, this creature was surprisingly easy to read. Eren was frightened. The thought of being left all alone was making him uneasy, worried about being forever trapped and isolated in that tiny little rockpool. Levi swallowed, the merman’s sad clicks and whines tugging at his heart and filling him with a sudden sense of responsibility. What if someone else found Eren? Levi would like to think they’d kind to him, but he knew from experience that the world wasn’t such a nice place. Grey eyes shifted to Eren’s swishing tail. Would he even be able to get out of there on his own?

  
Levi frowned. Now that he was thinking about, he would prefer to make sure Eren got back to the ocean safely. His mind would be haunted by unpleasant possibilities if he didn’t. And why not? Levi liked the beach, and spending time with a merman was far more interesting than going home to an empty apartment. Not to mention how breath-takingly beautiful Eren was. It would be a pleasure to sit here and watch him until the tide came in.

  
Levi went back over to the edge of the rockpool. Trying to sound calm and reassuring, he crouched down to look into glistening green eyes. “Don’t worry. I’ll stay with you.”

  
Eren inspected Levi’s face now that it was close by, idly tapping his small claws against the rock he was leaning on. He got the message after a while, trilling happily as reached out to grab Levi’s hand and pulled it towards him, placing the palm flat against his bare chest.

  
Clueless, Levi simply let it happen. He couldn’t deny that he enjoyed touching the merman’s golden skin. It was soft and surprisingly warm, the repetitive thump of Eren’s heart laying just beneath his fingertips. Considering the intimacy of the gesture, Levi assumed Eren was trying to thank him in some way. Or at least he did, until a tug on his arm threatened to pull him into the water. “No, I don’t thi…” Levi trailed off at another pull on his arm, biting his cheek as Eren’s hopeful eyes were shadowed by fluttering lashes.

  
Are mermen supposed to be so friendly?

  
As Eren managed to pull him half way over the edge, Levi’s eyes searched the rock-pool for anything dangerous. There were a few nasty crustaceans that lived around here. Thankfully, the only forms of life in the pool were darkly coloured algae, billowing like ribbons in the water, and perhaps a few gross but otherwise harmless snails. Levi stood up, granting the merman’s wish by carefully stepping over the rocks, cringing as the material of his pants became saturated. It didn’t matter, he had spare clothes and a towel in his car. The water barely reached Levi’s knees in the deepest part, which wasn’t so bad.

  
Eren enjoyed having company in the rock-pool, made apparent by his cheerful whistles and bobbing head. Quieting down, he watched Levi pluck a few pieces of dead algae from the water and toss them out onto the sand. With an innocent smile, Eren submerged the flukes of his tail before flicking it upwards, hurling a bucket load of water into the air.

  
Levi lifted his arm to shield his face from the downpour. It wasn’t very effective, his shirt and hair becoming soaked. He glared down at the merman with unimpressed eyes, while Eren simply clicked and tapped the water with his tail, not at all sorry for his behaviour.

  
Seeing as he was already soaked through, Levi begrudgingly sat down, rippling water now reaching his waist. It wasn’t cold, heated by sunshine throughout the day. Relaxing almost. Eren made another sound of approval and flopped down onto his back, spreading his arms out to make a T shape in the pool, the restricted space making his tail flukes crumple by the rocks.

  
This was a very strange day. Levi just wanted to walk on the beach, and now he was splashing around in a paddling pool with a stranded merman. As thinking about it only served to bewilder him, Levi tried to forget about how insane this entire situation was and enjoy it while he could.

 

 

Eren gurgled in the water, the discoloured gills on either side of his neck flapping open and closed as he tried to float on his back, strands of chocolate brown hair rising to float in a halo around his head.

  
With the merman splayed out like that, Levi couldn’t stop himself from staring at his exposed chest and abdomen. Eren was toned but not overly muscular, lean, the sploshing water running long the dips and curves of his sun-kissed body. Levi felt shameful checking-out someone that wasn’t even the same species as himself, but Eren’s upper-half was barely distinguishable from that of a human, his aquatic origins only given away by some relatively minor details.

  
Levi’s eyes shifted to the muscular yet slender emerald tail. There was no telling what was going on down there other than the rows of tiny iridescent scales and a few pairs of miniature fins. He didn’t know much about fish biology, but it was certainly very pretty. Levi particularly liked the way it faded into Eren’s skin, the speckled scales gradually becoming sparser until they stopped completely, although there were a few smaller ones dotted around his torso. Some were a bit bluer than the rest, which was interesting.

  
Catching his gaze, Eren whistled lowly as he paddled towards Levi, using his dexterous hands to grab the submerged rocks and pull himself along.

  
Levi tensed a bit as Eren approached, finding his turquoise gaze somewhat predatory. What did merfolk eat? Fish, right? Seaweed? Anything but humans?

  
Eren came close and trilled playfully, perhaps picking up Levi’s concerns, finned ears flicking back and forth as his torso rose up.

  
“Hey,” Levi greeted as Eren came to rest next to him. He propping himself up against the rock as drops of liquid rolled down his face, continuing to stare with fascinated eyes.

  
Levi idly swished his hand under the water. It seemed like Eren wanted something from him, but trying to figure out what would likely be a tiresome and futile endeavour. Instead, he gave Eren a small smile, then received a response in the form of a melodic warble. It was high but not grating, the chiming sound actually quite pleasant to Levi’s ears.

  
Eren gave a clipped chirp before he slid to the side, his whole body flopping into the pool with a giant splash. On his back again, Eren gently paddled with his hands until he was floating across Levi’s lap, then proceeded to flick some more water in his face.

  
It Levi wasn’t so distracted, he might’ve thought that Eren was trying to drown him. The merman stared up at him with wide doe-eyes, whistling softly as he snaked a hand around Levi’s wrist and brought it his chest again.

  
“What?” Levi tapped his fingertips against the merman’s wet skin, considering. Eren hovered in his lap, using his tail to wiggle back into place whenever he started to float away. Did he want to be petted? Levi raised an eyebrow, finding the idea ridiculous. Although... he had no clue what Eren would like. Levi’s mind was changed when his hand was placed at the bottom of Eren’s abdomen, his fingers absently running over the mosaic of smooth emerald scales.  


	2. Part Two

Eren’s scales were fascinating. The few on his hips had an irregular oval shape, flat and raising out of the skin as if they were embedded in it. Levi enjoyed the feel of them, each one a gentle bump beneath his fingers as he traced their edges, smooth and shining like polished gemstones.

  
Eren seemed to like it as well. A soft hum left his throat, eyes hooded and blinking lazily as he floated in the water, due to both natural buoyancy and the support of Levi’s legs on his lower back. Eren laid a hand on his stomach, flicking away a blade of seaweed before it came to rest across his ribs.

  
The merman was clearly relaxed, so much so that Levi half expected him to start purring. Considering as how trusting Eren was, it was fortunate someone with less compassion hadn’t found him first.

  
Grey eyes shifted to Eren’s peaceful face. His long ears fanned out in the pool, still and calm. They were undoubtedly the most alien feature of his upper half. Mottled with pale green, a fin-like webbing stretched between several barbs of cartilage. Levi reached up to feel them, the thin ears twitching and flickering around in the water at the faintest of touches. It went on until Eren jerked his head away to express his discomfort. “I guess you don’t like that,” Levi spoke out of habit.

  
Eren replied with a whistle, the frequency raising and falling a few times, while his slender tail undulated with enthusiasm. He blinked up at Levi, incomprehensive but still smiling. The only logical explanation was that he enjoyed the sound of Levi’s voice.

  
It was nice to think Eren might be able to understand some things based on his tone, but Levi tried not to get his hopes up. He wasn’t the most emotive speaker.

  
Going back to his investigation, Levi moved his hand to sweep away stands of floating brown hair, revealing the merman’s neck and half-submerged gills. There were three on the side Levi could see, presumably mirrored on the other, little grooves with flaps of darkened skin. Levi gently traced one of the lines with his fingertip. Eren didn’t mind having them touched as much, perhaps because they weren’t currently in use. He did squirm though, squeaking repetitively as he wiggled, tail flukes swishing around in the water. Ticklish, maybe?

  
Eren barrel-rolled out of his lap, flinging himself sideways into the middle of the rockpool. Levi couldn’t help chuckling as Eren tried to orientate himself, letting out a few final squeaks as he popped out of the water again and shook his head, removing the strands of hair that were clinging to his face. Levi no longer cared about being splashed with water. He simply squinted, letting the fine droplets spray over him.

  
When Eren was finished being a sprinkler, he laid on his stomach and started wading around in the pool, head tilting back to watch a flock of seagulls soar through the sky.

  
Levi observed while wondering if he would tell anyone about this experience. He supposed there wasn’t much point, no one would ever believe him. Even the most insane of his friends would think he’d lost his mind. It was probably for the best, though. There must be a reason no one ever found proof that these creatures existed, at least not as far as he knew. Eren’s kind must be hidden somewhere in the ocean, a place far away and undiscovered. He wouldn’t be the one to expose them.

  
Once it was over, Levi would probably have trouble believing it himself.  

 

 

A soft warble brought his thoughts back to the present. Eren sung sweetly, his shimmering tail languid as it swayed in the water. Levi found it impossible to look away, captivated by the merman’s vibrant colours and sleek body, watching intently as Eren raised a hand to sweep back his sopping wet hair.

  
It was without a doubt the most beautiful thing he’d even seen.

  
“Eren,” Levi said despite his suddenly dry throat, water dripping from his fingers as he held his hand out.

  
Eren responded to the beckoning voice, clicking twice in a row before he slid fully into the water and made his way back to Levi, ears tucking up and fanning out as he paddled over.

  
Levi fidgeted a bit as the merman reached him, those bright turquoise eyes warm and inviting. There was no harm in taking a closer look. 

  
Unexpectedly, Eren spun and manoeuvred himself until he was sitting in Levi’s lap on a slight angle, back against Levi’s shoulder and tail draped across his legs. The water held most of his weight, thankfully, the curve of his hips only a subtle pressure on Levi’s thighs.

  
The intimate position left Levi at a slight loss. Looking to the side, he saw webbed ears flutter a bit before Eren met his eyes, a gentle cooing noise leaving the merman’s parted lips. The reassurance was comforting. Levi glanced down at the emerald tail swishing in front of him, long and slender, the appendage practically begging to be touched. His hand moved to Eren’s hips, returning to the place it had been earlier, the rounded scales glinting as they peeked out of the water. 

  
Levi shifted his hand a bit further down, tentative fingers examining the larger scales on Eren’s tail. The sunshine bounced off them in differing shades of bluish-green, colours that would look stunning while swimming around in the sea. They overlapped quite a bit, each one tapering to a blunt point that protruded ever so slightly. The scales weren’t slimy but had a glossy sheen to them, wet and slippery, more like a thin coat of oil than anything else. Levi didn’t mind at all. It was far more pleasant than he’d expected.

  
A set of fins laid just below Eren’s waist, currently tucked away and resting flat against his scales. Levi grabbed the end of one between his fingers, lifting it up to extend the sheer webbing. It was held together by thin rays of cartilage, much like Eren’s ears and flukes, able to fan out whenever they were needed. Pelvic fins, Levi thought. Although he wasn’t sure if his high school biology class was applicable to mermen.

  
Releasing the fin, Levi went back to the glimmering tail. Everything about it was so foreign. The unreality of it was more than enough to hold his fascination. Levi was unable to stop himself from exploring further, entranced and out of his mind with wonder. There was a thin crease on the front of Eren’s tail, only a few inches down from where it began. He reached out to trace it with his index finger, the strip of scale-less skin silky beneath his touch. Curious and unaware, Levi gently stroked the crease, assuming it must be a gill of some kind.

  
It wasn’t until a subtle pressure caused his finger push past the fold of skin and dip into a fleshy opening that Levi realised his mistake. Panicking, he removed his hand from Eren’s sex and shuffled out from under him, the hasty retreat making shallow water turbulent. “I… I’m sorry,” Levi apologised sincerely, huddled up against the rocky wall of the pool.

  
As embarrassed as he was over the mistake, he was even more concerned that Eren would be angry or upset over the intrusion. The merman clearly possessed human-like intelligence, that much was obvious from his expressive face and attempts at communication. He was no doubt capable of rational thought and understanding. Eren deserved the same respect as any other person, not to have Levi sticking his fingers where they didn’t belong.

  
Eren’s tail slapped against the pools surface, its impact causing tiny droplets of water to spray over them both. He didn’t seem offended at all. In fact, a string of high squeaking sounds led Levi to believe that he found the situation quite amusing. Which was… a surprise.

  
For some reason, Levi had thought merfolk wouldn’t have any genitalia. Those sorts of details were never shown in movies, and there was never any need for him to research the physiology of a believed to be non-existent creature. It made him feel a bit silly. Of course, it was only natural for them to have _something_.

  
But now that he knew it was there, Levi couldn’t help being intrigued by it. Was it human-like? The opening was in a grey area between tail and torso, any guesses he could make would be exactly that. Would it resemble anything he was familiar with, or something entirely different? It was weird to think about. It also occurred to him that Eren had done absolutely nothing to deter the sexual contact. Eren’s positive reaction put a few strange thoughts in Levi’s head, whether they were wanted or not.   

 

 

Eren’s chortling soon came to an end, turquoise eyes quickly finding Levi again. His gaze was curious and analytical, a knowing eyebrow raising on his face. Eren whistled and clicked as he sunk back into the water.

  
Levi watched his submerged figure, Eren’s agile hands searching through the sand and rock. It took a moment for Eren to resurface, bubbling as he flicked water out of his ears, then started making his way towards Levi a gentle swish of his tail.  

  
Levi’s jaw clenched, still thinking of the merman in ways that he probably shouldn’t. Eren was irrefutably attractive, if he’d seen him in a coffee shop or someplace else, Levi was sure he would’ve tried to approach him. The tail was a bit of an issue. While beautiful and enchanting, it also raised a few questions and concerns.

  
Once in front of him, Eren warbled in a high tone as he held his hand out, a small black object gripped between his fingers.

  
Levi squinted at it, the dark surface smooth and glossy, spiralling to a subtle point at the top of it.

  
A snail.

  
Eren clicked happily, his hand waving about in Levi’s face. Was it a gift? He reached out to pluck the tiny offering from the merman’s hand. “Uh… thanks,” Levi said with some confusion, taking a moment to inspect the shell before placing it on top of a nearby rock. It was nice, but he didn’t have much use for it.  

  
Eren let out a melodic whistle, pleased that his gift had been accepted. His head tilted at Levi, eyes questioning, before he started twisting around in the water. After adjusting his tail, Eren successfully managed to place himself in Levi’s lap once again, sitting in the same position with his back against Levi’s shoulder. Dark green flukes flicked up to shower them both with a light spray of water. 

  
By this point, Levi was more than a little bit suspicious. He'd thought Eren was being unusually friendly, and had dismissed it as nothing more than gratitude. But now he was convinced Eren was trying flirt with him.

  
Levi’s eyebrows furrowed. He never imagined he would be interested in such a thing, and yet here he was, not at all put off by the idea. Eren was gorgeous, and so long as they both wanted it… Levi didn’t see any reason not to try a few things. It wasn’t like anyone would ever know.

  
A hand on his face made Levi blink. Eren brushed his knuckles along Levi’s cheek, his fingers eventually shifting up to card through his wet hair and trail along the back, apparently fascinated by his undercut. The short claws brushing along his scalp felt quite nice. While Eren entertained himself, Levi took a risk by putting his hand back on the merman’s tail. He adjusted a pelvic fin that was sticking out oddly, then ran his palm down the side of Eren’s tail, emerald scales rough against his skin on the way back up.  

  
Eren clicked as his hand fell from black hair, using it to hold onto Levi’s shoulder and prevent himself from floating away. The flukes of his tail slowly swished from side-to-side.

  
Levi took it as a sign of enjoyment, although he was still hesitant to do anything more. It was hard to know what was okay when your partner couldn’t understand you at all. Eren seemed to pick up on his reluctance and warbled lowly, lifting the end of his tail to splash him in the face. Even with the playful act, Levi still felt nervous. He had no idea how this would work or what would happen, or if it was even physically possible. He supposed there was only one way to find out.


	3. Part Three

**Notes for the Chapter:**

> Please be advised that this chapter is mainly merman smut. 
> 
> Who am I kidding? This is probably what you signed up for.  
> 

Levi ran his hand along Eren’s tail as he tried to organise his thoughts, and he was taken by surprise when the merman decided to act first. Eren reached down to touch himself, running his fingers along the slit Levi had discovered earlier, hand brushing down either side of it before he swept a single finger over the thin crease.

  
“Shit,” Levi whispered, watching the merman’s actions with wide eyes. Eren stroked himself some more before he put a finger on either side of the slit and spread it open, displaying the subtle pink flesh that laid within. While Levi wasn’t entirely sure what he was looking at, he was definitely getting turned on by it.

  
Eren sung in a sultry tone, moving his hand away to let it rest on the side of his tail.

  
Levi swallowed as he reached out to take over. He stroked his hand over Eren’s sex, the scale-less skin smooth and velvety. It felt a little different now that he knew what it is. When the merman made a chirp of approval, he got a bit more confident. Levi rubbed two fingers along Eren’s slit, following the centre line all the way to the bottom and then back to the top. After a few passes, Levi allowed his middle finger to sink into the parting and slowly ran it between the fold of skin. It was soft and wet inside, hot, the flesh silken around his fingertip.

  
As he couldn’t see what he was doing very well, Levi decided to take the exploratory route. His finger slipped further in, very carefully feeling around inside Eren’s sex. There was a bulge towards the top, something round and spongey, and so Levi used a light pressure as he circled his finger over it. Eren let out a soft whistle as the end of his tail flicking around in the water, a sure sign that he was enjoying it.

  
Levi left the mysterious lump alone and slid his finger down Eren’s slit, the skin parting slightly around his knuckle. At the bottom was an opening, a small hole surrounded by muscle. He could make an educated guess of what that was. Putting his free arm around Eren’s waist to hold him steady in the water, Levi gingerly stroked the hole before pushing against it, letting out a shaky breath as his fingertip slid inside. It helped that Eren seemed to be naturally lubricated, a trait that was probably meant to keep him from drying out while on land. Levi managed to get his whole finger in without much resistance. There wasn’t anything abnormal about it from what he could tell… except perhaps the walls being particularly muscular.

  
As the merman wasn’t showing any signs of discomfort, he pulled his finger out before pushing it back in, slowly, another pleased sound falling from the merman’s lips.

  
“You like that, don’t you?” The words were redundant, but he enjoyed saying them just as much as someone might enjoy hearing them. Levi steadily slid his finger in and out of Eren’s hole, stroking the rim with a second one until he managed to get it in as well. Eren stretched with ease, his wet entrance eagerly taking whatever was given, and it wasn’t long until Levi was spreading his fingers apart to prepare him for a third. Eren was whistling out of pleasure, head lolling back as his tail twitched in the water.

  
Levi found that he was able to reach the lump at the top of Eren’s slit with his thumb. He started to circle over the top of it as he continued fingering him, but a sudden shift made Levi pause his actions. It felt as though something was moving beneath his thumb, which initially caused him a fair amount of concern. Looking down at Eren’s slit, his eyes widened when saw something fleshy emerging from the parting skin. It continued to extend until the full length was exposed, flushed pink and glistening with slick liquid, almost identical to a human penis.

  
Levi was stunned by the new development. He ran a finger up the underside of Eren’s cock before taking it in his hand, the merman starting to click and chatter as he stroked it. The skin was smooth and slippery, coated in the lube from Eren’s slit.

   
At this point, Levi was questioning why he hadn’t taken his clothes off before getting in the water. His own cock was straining beneath the wet fabric, his hips lifting to grind into the rear of Eren’s tail as the merman wiggled in his lap, tail pushing back and undulating against his crotch. Levi groaned at the friction, stroking Eren once more before his hand dipped back into the slit. Searching fingers soon found the opening and pushed inside, the muscle stretching taut as he as added a third. Levi wasn’t so gentle this time, his fingers moving fast as they slid in and out of Eren’s tight hole, panting from his own arousal.

  
Eren let out a whine before slipping out of Levi’s lap and back into the water. He warbled a soft song as he drifted along on his back, seductive turquoise eyes framed by wet and unruly hair.

  
Water splashed as Levi rushed to follow. He laid next to him in the shallowest part of the pool, on his side to face the merman. Eren seemed impatient as well, his hand quickly reaching out to palm at the hard bulge in Levi’s pants, although he had some difficulty getting them undone. Levi gladly took over, fumbling with the button and fly before pushing his pants down and off. It took several frustratingly long seconds to peel the wet material from his skin.

  
Levi bit his lip as Eren reached out to touch his cock, gently racing the head before running his hand along the length as he examined it. Thankfully, the merman took care to keep his claws well out of the way. Eren leisurely stroked him, ears flicking as a high trill emanated from his throat, pleased and impressed with what Levi had to offer.

  
Levi was done questioning it. Right now, all he knew was how desperately he wanted to fuck Eren. 

  
As if reading his mind, the merman moved to settle in the shallow water, laying flat on his back while his tail flukes swayed expectantly, a low warble leaving his parted lips.

  
Levi rolled to hover above Eren, his brain working to figure out the easiest position. He ended up with a knee on either side of Eren’s tail and one hand on the ground to support himself, using the other hand to guide his erection. Levi lowered himself, rolling his hips to slide the head of his cock up and down the wet slit before prodding at Eren’s opening. Levi started pushing inside, Eren’s muscles tensing and relaxing as they tried to coax him in further.

  
“Fuck,” Levi groaned as he fully sheathed himself, his cock hot and throbbing inside Eren. The pleasure was mind numbing. It was so tight, the powerful muscles of Eren’s tail contracting around him in a massaging motion. Levi pulled out to the tip before slowly pushing inside again, the wetness of Eren’s slit allowing his cock to slide in without too much resistance, then repeated it until he found a steady pace, his movement causing the water to ripple and swell around them. Emerald scales lightly scratched against Levi’s thighs with every thrust, but fucking Eren felt so good that he barely noticed.

  
Eren whined and whistled, the closest thing to a moan he could produce, back arching in the water to angle his slit so that Levi’s cock could as deep as possible. One his hands moved to claw at Levi’s lower back, encouraging him further.

  
The scratching at his back made Levi speed up, pants and groans mixing with the audible slap of his hips against Eren’s tail, his thrusts becoming wild and frantic as Eren shamelessly keened for more. Levi vaguely registered the feel of tail flukes coiling around his ankles, water splashing in his face as Eren writhed in pleasure, practically mewling as got fucked hard and fast.

  
“I’m gonna come,” Levi panted, forgetting in his delirious state that Eren couldn’t understand him. “So close… Fuck, you feel so good.”

  
Eren replied with a disjointed whistle, his hand moving down to grab Levi’s ass and hold him close. Eren’s tail suddenly thrashed, twitching in the water as he made a high-pitched sound, the merman’s cock squirting sticky white liquid onto both their stomachs. The clenching of Eren’s hole was unbearable, and Levi only got a few more thrusts in before he was coming as well. Levi moaned as he shoved him pulsing cock deep inside Eren, mindlessly grinding against Eren’s slit as he filled the merman with a generous load of his cum.

 

 

Once it was over, Levi’s arm gave out and he flopped down onto Eren, spent and exhausted. Eren sung softly as his tail flukes released their hold on Levi’s ankle. He seemed satisfied, warbling as he raked his claws through Levi’s hair, carding through the wet strands with adoration.

  
Levi floated in the water, head on Eren’s chest as he stared out to sea. The sun was only just beginning to set. There was still time before the tide came in. Lifting himself up again, Levi pulled his softening cock out of Eren, the slit neatly closing behind him, then leaned down for a kiss. Eren turned his head away. He wasn’t offended by it, Eren obviously liked him. Perhaps kissing simply wasn’t something merfolk did.

  
Eren clicked as his tail lazily swayed in the water, head tilting as curious green eyes flicked over Levi’s face. He smiled, reaching out to stroke Levi’s cheek with the rough pads of his fingers.

  
Levi sighed with content as he went back to laying on Eren’s chest, who immediately started petting his head as he sung a soft tune.  

  
The delicate scrap of claws on his scalp was strangely relaxing, as was the gentle chiming near his ear. It was almost as if the merman was trying to lull him to sleep.

  
The water in the rockpool started to turn cold as the sun got lower. Levi continued to lay there, the thought of moving not crossing his mind even when he started to shiver. He watched the ocean with heavy, slow-blinking eyes, the lapping waves turning golden sand brown as they crept ever closer.

 

  
He wanted to stay with Eren forever.

**Notes for the Chapter:**

> **FIN**
> 
> (ha, ha. get it? sorry)
> 
>    
> Comments are appreciated!   
> [My tumblr](https://fluffyboots.tumblr.com/)


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